Leak standard



J. A. ROBERTS LEAK STANDARD April z5, -1961 2 Sheets-Sheet 1 lnvenror John A. Roberfs M/Qi 26%,

His Arorney Filed July 11, 1957 Aprxl 25, 1961 J. A. ROBERTS 2,981,091

LEAK STANDARD Filed July 11, 1957 2 sheets-sheet 2 FI G. |nven+or1 John A. Rober'fs His AHorney '2,981,09l Ice Patented Apr. 2s, 1961- LEAK STANDARD John A. Roberts, Lynnield, Mass., assignor to General Electric Company, a corporation oiv New York Filed July 11, 1957, Ser. No. 671,265

Claims. (Cl. 73-1) l My invention relates to aleak standard,4 for calibrating 2 leak rates as small as lying of an ounce per year. A typical leak detector comprises a detector unit and a control unit. The detector unit, sometimes in the form of a hand gun, contains the sensitive diode element and an impeller unit which is used to draw air through a probe or search tube by which it is supplied to the interelectrode space of the diode. The response of the diode to the presence of halogen vapors is made evident on the control unit which is electrically connected to the detector unit and provides means for adjusting the sensitivity of the diode and for giving a meter indication of a detector in which air is supplied through a probe `orV j search tube at a predetermined rate to an element which issensitive to a tracer gas and provides a comparative indication of the amount of the gas normally present in the air to that which is present at a leak through which the tracer gas is supplied into the air. In order to obtain a quantitative Vevaluation of the magnitude of a new leak, the response of such a detector to this leak must be calibrated against a standard adjustable leak which can be set to provide controlled rates of leakage which are adjusted to givethe same indication on the detector as was obtained at the new leak.

My leak standard is particularly suited for calibrating a detector rsuch asv described and claimed in United States Letters Patent 2,550,498, Chester W. Rice, granted April 24,1951. This Rice apparatus may be used for detecting substances such as certain gases, vapors, smokes, and similar matter inan atmosphere by noting the increase in current flow between the electrodes of a diode due to positive ion formation at its heated anode inthe presence of`saidsubstances. The sensitivev diode element of the apparatus responds to certain types of substances such as the alkaline metals or other sub-` stances having ionizing potentials less than the electron work functionV ofthe electrodes, the halogen's, or compounds 'of'eith'en ForY certain substances, such as the alkaline 'metalsfand their compounds, the ion formation apparently occurs by ionization of the substance when it comes int'ocontact with the more positively charged 'and heatedfelectrodeof the diode. For others, such as the halogensandgtheir compounds, the substances appear to'v cause'` ionformationonlytin the presence" of whatrmig'ht bel called sensitizing materials, such as the "alkaline metals 'and their compoundsgand it further appears in this case that'Vv theV sensitiz'ingfmaterials, themselves `are V.actually t ionized tofattord the desired positive ion currfent.

f The apparatus of the/Rice lpatent hasl been used for detecting leaks in pressure systems as welll 'asgleaks' in vacuum systems'.l Y 'In' either case, a` traoerrgasor sub.-

stance tol "theifdi'ode of the apparatus isv'sensitive is used "forlocating'theleak.,` Whrififused inf-detecting leaks intpressu're systems, theftracer gas is'f supplied iin- ,"1"

der presvsu'reito the systems an'dfthe suspected areasV of thesystem are examined,` by `a "searchl tube or probe; through'which the'jgasbeing'tested isls'ckd in Aand supplied between the electrodes 'ofi the e. diodei l When the" suction end of thefsearchtube passes {Ji/ferretl leak, `the presence of .thezleak is Virlldicate'd Abythe increased ckoiilpc-A tivity'ofthe ,diode dueto the'presenceroffthejracer gasa is usuallya V halogencontaining gaslsuchgasudi chlorodiiluorgr'nethane vaporrL-{Since the tracer;gasif'most` commonlyenployed for detecting .leakstis a. halogen f compoundythe apparatus has been rcor'nrnonlyrefe'rrevdf.,V

to asraf halogen leak detector;

detectors 'are' very" the change in diode conductivity when exposed to halogen vapors of different concentrations. The control unit also embodies a balance control whereby the detector may be-fzeroed in accordance with the amount of halogen Vapor normally present in the air. After the detector has been zeroed, the gas from a leak supplied to its sensitive element through its probe will provide a meterindication on the control unit which is its comparative response to the amount of gas normally present in the e air and that present at a leak through which the halogen gas is being discharged. One form of such a device is illustrated and described in the Proceedings of the I.R.E. for` August 1950, beginning on page 852 in an article entitled' Positive-Ion Emission, a Neglected Phenom'v enon, by W. C. White.

A calibrator for such a halogen leak detector must consequently provide means for supplying in succession through the detector probe and to its sensitive element puried air and puriiied air containingan adjustable and metered amount of halogen vapor. Since the sensitive diode element ofthe detector has substantially a linear response under its conditions of use, the difference `in conduction of thel sensitive element between 'zero vsetting and a leak detection response can be duplicated in the calibrating apparatus by obtaining a like change in conduction of the sensitive element` and then determining from the calibration apparatus the weight flow of halogen' gas or vapor which is productive of this change.

It is an object of my invention to provide a standard the inlet end of a capillary tube having ,a bore ofriixed andlpredetermin'ed dimensions.

j 'Itv isy a further object of myinvention to provide apparatus in which purified air and purified air containing j l 'a metered quantity of a gas or vapor arealternately supplied to a receptacleefor thevnozzle of a test instrument Atheaccompanying drawings inlwhicli'fa preferred er'nbodii-` vment thereof has been illustrated.

standard embodying myinventiomA Y whose comparative responseto suchfa gas or vapor is to be; determined quantitatively. v Y It isranother'objet ofrmy invention to provide a pre Y cision device which may be used to calibrate and zero a.

halogenv leak detector. y

i My invention, ltogether"with` further objects `and Yad-l' vantages 'thereof,".willibe'st be'understood-by reference tothe following specification takenjn connectionwith f In thefdrawings, vt f Figs; u1 is alperlspective vVie'vv'illu'strating, inVtheir-,physi-l l leak' cal frelationship, the'severalelements of `a halogen V'Fig 2v isadiagraminatic representation of theapparal' .t "ltusshown Ain Fig. 1v and'of`the 'relationship of suchl ap-` paratus'to the'detectorlunit of a-halogen leakdet A' y whic'h is to be calibrated andaeroed'thereby;

of Fig. 1; and

Fig. 4 is an enlarged showing of the divider assembly of Fig. 2.

The leak standard shown in Figs. l and 2 is'made up of a halogen vapor system and a purified air system. These two systems combine to provide an adjustable halogen leak. T he magnitude of the leak is indicated on a gauge which is provided with a leak rate scale.

The purified air system consists of two vibrator type air pumps 1 and 2iwhich supply air through pipes 3 and 4 to filters 5 and 6. The discharge openings in these filters are connected in parallel to a shut-olf valve 7 which controls the fiow of filtered air through a pipe 8 connected to a divider assembly 9 by means of which filtered air is supplied 4to selector valve 10 and, througha pipe 11, to a standard leak assembly 12. As indicated in Fig. 4, restrictions are provided in the discharge branches of the divider assembly to secure the desired division of air flow to valve 10 and to leak assembly 12.

The vibrator pumps are of a type used for supplying air to household aquariums and comprise a mechanism having a vibrating armature 13 which operates a Aflexible bellows 14 into which air is drawn and from which air is expelled through a flap valve mechanism 15. They are mounted on sponge rubber pads 16 so that their vibration will not be transmitted to the other parts `of the apparatus. They are also provided with an adjusting screw 17 for controlling the action of the vibrator mechanism. This mechanism is of the usual electric type Vand is. provided with a coil mounted in a magnetic, structure 18 ofwhich armature 13 forms a part. This coil is connected to` a source of electric supply by a circuit and switch not shown in the drawings. These air pumps are commercially available under the trade name fBel-Bul and are sold in this country by Aqua Air Products of Miami, Florida. They are capable of supplying about two Vcubic feet of air per hour at about one pound per square inch pressure. Obviously, pumps of different construction may be substituted for those illustrated. The filters and 6 are replaceable cans containing activated carbon which will purify the air supplied therethrough by removing from it halogen vapors and other vapors or gases to which the leak detector is sensitive.

The halogen vapor system comprises a halogen vapor supply tank 19 which is connected through a -pipe 20, a shut-ofi valve 21, a pipe 22, and increase Valve 23 and a pipe 24 to a pressure chamber 25 not shown in Fig. 1 but indicated in Fig. 2. This pressure chamber is a manifold, providing a common connection for pipe 2 4, the pressure pipe of the pressure gauge v 26, andpipes 27, 28, and 29. Pipe 27 is connected through decrease valve :3 0 and a pipe 31 to a support fitting 32 provided with a dischargenippie on which one endofa long flexible tube 33 is connected. Pipe 28 is connected through a fltting34 to a ballast tank 35 whose function is to main-l tainsubsta'ntially static the pressure in the pressure cham# ber.v This fitting 34 includes, as part thereof, afrangible inetalldiaphragm `fuse whichwhen ruptured permits a discharge of lvapor from the vapor'system Yto the surrounding air. This fuse provides protection for the pressurefgauge 26 which is constructed to indicate amaximum'pres'sure of ten vpounds per square inch, Whereasthe pressure.' of. the yap'or inthe supply tank. 19 may be as high as eighty poundsor more.4 This supply tank is provided'with a fitting 36 and-'valve 'fyvhich is-,connected to a pipe :37 (Fig` 2) by means of which the'supply tank L1 9 maybe recharged with a gas or a liquid Vaporizableat room ternperatures, such as dichlorodifiuorometharie; commonly known under the trade name of'Fre'o'n l2. Pipe 29j-is connected through a `'Hitting 3S Yto thestandard leak The standard leak'assemblyV discharges through a def l tachablev test connection by-pass 3,9 and' a pipe 4])into'v selector' valve lof The' Seltor vatte Ymay .be 'nos'risalenti..

4 r shown, mounted on its spindle 41. In the zero position, this selector valve supplies purified air through a pipe 42 to a receptacle or gun fitting 43 in which the nozzle 44 (Fig. 2) of a detector unit 45 of a halogen leak detector is positioned during a Calibrating operation. In this same zero position, the mixture of halogen vapor and its carrier of purified air, which is supplied through pipe 40 to selector valve 10, is discharged to the surrounding air through the valve and a pipe 4 6. In Fig. 1, this discharge pipe, as well as one of the branches of the divider assembly 9, havebeen displaced from the body portion of valve 10 in order to provide a better illustration of the structural arrangement but it is to be understood, as indicated by the dot-dash lines, that these parts are assembled and provide continuous passageways as indicated in Fig. 2. In the leak position of the selector valve 10, the halogen vapor and its carrier of purified air is supplied to gun fitting 43 through the valve and pipe 42 and the purified airfrom oner branch ofthe divider assembly 9 is supplied lthrough the valve'to exhaust pipe 46.

The increase and decrease valves 23 and 30, receptacle 43, gauge 26, detachable test connection by-pass 39, the operating'knob 34 for selector valve 10, and an electric switch for controlling the energization'of pumps 1 and 2 are mounted on or extend through the front panel ,of an enclosure in'which the other parts are located. 'The support fitting 32, recharge pipe 37 connected through valve 36 to fitting 36 of supply tank 19, and the discharge portion of diaphragm fuse fitting 34 are mounted on or extend through the back of this enclosure which is provided with a lid or cover that can be opened to pro,- vide accessibility to the various parts enclosed therein.

The standard leak assembly is shown in detail in Fig. 3. It comprises a mounting for a capillary tube 47 which extends lengthwise of a casing 48 into which the purified air is discharged through pipell. The conduit through this casing 48 and the bypass 39 constitute a mixing chamber into which gas is discharged from the capillary tube and mixed with the purified air supplied through pipe 11. When the nozzle 44 of a detector 4 5 is inserted into receptacle 43, it acts as a stopper and any surplus air supplied to casing 48 is discharged through a vent 49 in its side wall. The capillary is supported in position by couplings 50 and 51 and a pipe 52 which connect `one branch of T-fitting 38 to one end of casing 48. The fittings 50 and 51 engage the outside of the capillary tube'47 and form .a substantially gasftight fit therewith. Any leakage of halogen past the seal of fitting 50 will Abe discharged through openings 53 in this connecting pipe 52 and consequently cannot enter casing 48. t

Capillary tube 47 may be formed of glass and I prefer to use a borosilicate glass which is less liable to fracture due to temperature ychanges because of its small linear coeicient of Aexpansion.A It is provided witha vbore4 of about 0.003 inch in diameter which is reduced at 54,11ear its discharge end 55 to a size'vvhich is normally invisible to the naked eye. This reductionin size may be accom- 1 pusheaby heating the tube'at s4"w11t1e'hpldingtheperts thereof in alignment and allowing surface tension effects to neck in or decrease the bore size ofthe capillary while passing airtheretghrough. Capillariespf various sizes-may be provided andy I haveused capillary tubes which will provide'mass ow `rates of 0 to 0.1;,0 to 1.0, and() t o l0 ounces per year leakageof F-re'on lit'theretllroughV in Athe pressurerangeof 0%10 pounds 'per square inch o f Ygauge 26. Injfview'iof the varranger'nent'providedV whereby .the pressure of halogen gas `atthe .input end of the capillary tube 47 may be varied, itis quite obvious that the lea'k standard is 'jadjustablefby' adjusting this pressure toprovidevariou's ates'of discharge of' halogen atitheoutpu't end 'or tip '55 of the c'apillary'tube.` VBy having the restricjtionsat l54 n'earth discharge end ,of 'the'c'apillarytube 47, `.its .change in fiow rate'f'responds more rapidly! to changes of pressure at its input endwhich lis connected tg pressurerchamber 25. The-.tip end-550i thelcapillary tube is exposdawhsu .by-pass fitting o9` fis removed;-

Y its reduced size provides a convenient connection for a ilexible :tube by means of which a calibrator is attached thereto in order in turn to calibrate the leak rate of the capillary forming part of the leak standard.

The calibrator for the standard leak assembly may be of the type shown in my -application Serial No. 671,342, led July 10, 1957, and assigned to the same assignee as the present application, in which the displacement'rate of a short liquid column in a'capillary tube of calibrated volume is determined. The weight ilow of gas thereby determined for dilerent pressures on gauge 26 of the leak standard maybe applied as indications on the inner scale of this pressure gauge which is also provided with anv outer scale calibrated in pounds'pressure per square inch. This outer scale is employed when making use of the calibrator to determine the weight ow of gas through capillary tube 47 at various pressures. The inner scale of the leak rate gauge 26 is conveniently calibrated to indicateweight oW in .ounces per year at standard atmospheric pressure (29.921 in. of mercury at 0 C.) and at a room temperature of 25 C. If the ambient conditions diier from standard, a diierence of up to several percent may exist between the indicated and actual leakrrate. If maximum accuracy is desired, it will be necessary to make a correction which can be provided for by a formula and reference" charts so that the indicated leak rate shown by the pressure gauge can be converted into theactual; leak rate. f

vThe viscous laminar ow of gas through a cylindrical capillary is governed by the Poiseuille` law:

K 1l'ra/4.P2`2"'1312VV Nm- 1611 T Z` ROTH,

. wherein Nm is in moles per second, 4T is thecoeicient of viscosity at temperature T of the capillary, a and l are, respectively, the radius and length of the cylindrical capillary in centimeters, P2 and P1 are, respectively, the upstream 'and downstream pressures injmicrobars at the ends ofY the capillary, R0 is the gas constant, land T-m is the'te'mprerature at which the moles per second is measured. With the aid of thisformula, a pressure correction factor for differentY gauge pressures at di'erent barometric pressures may be determined and a temperature correction factor maybe determined for the ambient temperaf ture at time of measurement. With these correction factors, the corrected gauge indication WC1l for v'ambienti conditions Vof temperature and pressure will be the. leak` aesinet 6 receptacle 43 and that the impeller 614 driven by motor 62 is sucking air through nozzle 44, probe 60, andthe electrodes of the sensitive element 63 of the detector unit. With .the parts so positioned, the control unit of the leak detector is zeroed while it is being supplied with filtered air from the halogen leak standard. Thereafter, the selector valve 10 is operated to the position shown in Fig. 2 so that a measured quantity of tracer gas or vapor in a ltered air carrier is supplied to receptacle 43 and the indication of the instrument of the control unity of the leak detector is then observed to determine its' indication and response to this measured quantity of; halogen vapor. The rate of supplying halogen vapor through the halogen leak standard is then adjusted by either increasing or decreasing the rate of supply until itsj rate of supply causes the instrument of the halogen leakv detector control unit to give the same indication as was observed when detecting a leak, the quantitative maghitude of which is to be determined. The mass rate of flow of gas through the leak assembly 12 is controlled by vary-V ing the pressure of the vapor in pressure chamber 25 thereof. This is accomplished by cracking the shut-olfl valve 21 and cautiously operating the increase valve 23 with decrease valve 30 closed until the desiredpressnre is obtained. If the pressure in'chamber 25 is ltoo great, itmay be reduced by opening decrease valve 30 and venting the vapor through tube 33 to a remote locationA so that the exhaust of this vapor will not interfere with the Calibrating operation by any eiiect it might have onv the Ydetector unit of the halogen leak detector. During a leak calibration, the valves v2.1, 23, and 30 are closed and the pressure in the halogen vapor system is main-V tained static by the ballast tank 35.

If, duringvradjustments, the pressure limitations of the gauge 26 areexceeded, the frangible diaphragm fuse 34 will be ruptured. lf, due-to this rupture, or for any reason, air is admitted to the halogen vapor system, this must be removed by clearing the system of vapor through rate gauge reading W divided by the pressure lcorrection factor` ,Cp and the temperature correction Vfactor Kt, namely n L i t Warme Y The use of 'my halogen leak standard will be described Y Vso in connection with the, diagrammatic Arepresentation thereof shown in Fig. 2, which'also diagrammatically indicates,

the detector unit 45 of a halogen leak detector.

It is assumed that thevaporfsupply tank 19 is suitably charged with tracergas or halogen vapor, that Vshut-oit valve `21 and increase and decrease valves 23 and 30 are closed, that pressure chamber 25 and ballast tank.35 are'charged with vapor under pressure,-and thatthe motors and pumps'are supplying iiltered air through the two branches ofA the divider assembly 9 to one input port 560i A'selector valve 10,and tothe leak assembly 12 through pipe 11. It, is also to be assumed that input portV 565of valve 10 is connected by the relative position of theparts of valve 10 toitsoutput port 57 and that its input port 58 isconnected toits output port 59, so that filtered air-is'suppliedto receptacle-43 Vand theldischarge Ufrom leak assembly 12 is connectedo pipe 46 forY dis,-

charge to the-`surrounding atmosphere.` It will alsoY be v assumed that the fnozzle 44 ofthe probe 6,0 of thegun typ`jdetector-unit 45 shown'in Fig..2 is locatedf within a vacuum pump connected through tube 33 followed by the admission of vapor into the system from supplyv `tank 19 which operation is repeated several times until and it will Abe possible for air" to enter through the'leak Y capillary or the decrease valve, if open. y:k The filters 5 and 6 will need to bel replaced from time to Vtime and standards may be established for requiring such change when a desired ratio of the indication on zero. to the dierence inr indication from zero to leaktest is obtained. The usefulnessof the iilterr'swill be extended. if the air supply valve 7 is turned to the ol` position lwhenever the air pumps are not operating since this will; prevent halogen vapors from diiusing back into thesei filters from the halogen vapor system.

In order to protect'the halogen'vapor-system against damage from excess pressure being built up in the systeml dueto increases in ambient temperature, the ballast tank and the vapor supply tank lmay be provided with fusible plugsr which will melt at a-certain temperature at which this rdangerouscondition might exist.

It is quite obviusrthat'various modiicationsnmay be made in the particular halogen leak vstandard above described without departing from the spirit and .scopelof my invention and I consequentlyY contemplate, in the apf. pended claims, to cover all such modifications asA come,

withinthe true spirit and scope of my invention.' fIliefse'Y modilicationsmay involve changes inthe piping a'rr'angement, the arrangement of`p'arts, or thesubstitutionjof equivalents Aforparts" shownv in'the',drawingsV a dde?,L

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A standard leak assembly comprising a conduit, a capillary tube having its discharge end located in said conduit, means for supplying gas at an adjustable and substantially constant pressure to the other end of said capillary tube, means for filtering air to remove said gas therefrom and for supplying said iiltered air at a desired rate through said conduit past the discharge end of said capillary tube such that the air acts as a carrier for said gas to the exit end of said conduit, the internal dimensions of said capillary and said pressure being related such that the mass rate of flow of said gas may be accurately varied by -adjusting the magnitude of said pressure, and means responsive to said pressure, said responsive means being calibrated to provide an indication related to the mass rate of flow of said gas.

2. A standard leak assembly comprising a conduit, a capillaryV tube having its discharge end located in said conduit and having a restriction in its bore near its discharge end, means for supplying gas at an adjustable and substantially constant pressure to the other end of said capillary tube, means for supplying filtered air at a controlled rate through said conduit past the discharge end of said capillary tube to an exit end of said conduit remote from said gas supply means, and a receptacle at said exit end adapted to receive the nozzle of a test instrument.

3. Calibrating apparatus comprising a pressure chamber, means for supplying a tracer gas to said pressure chamber and for adjusting the pressure of said gas in said pressure chamber, a mixing chamber, a capillary tube connecting said pressure chamber with said mixing chamber, a lter for removing said tracer gas from the surrounding air, means for supplying the surrounding air at a desired rate through said lter and said mixing chamber to a discharge opening, the internal dimensions of said capillary and said pressure being related suchV that the mass rate of iiow of said gas may be accurately varied by adjusting the magnitude of said pressure, and

means responsive to said pressure, said responsive means.

being calibrated to provide an indication related to the rate of ow of said gas. v

4. Calibrating apparatus comprising a pressure chamber, means for supplying a tracer gas to said pressure chamber and for adjusting the pressure of said gas inV said pressure chamber, means for holding the pressure of said gas in said pressure chamber at a substantially constant value, a mixing chamber, a capillary tube connectmg said pressure chamber with said mixing chamber, a filter for removing said tracer gas from the surrounding air, means for supplying the surrounding air at Va desired rate through said filter and said mixing chamber to a discharge opening, the internal .dimensions of said capillary and said pressure being .related` such that the mass rate of ow of said gas may be accurately varied by adjusting the magnitude of said pressure, and means related to sd pressure to indicate the rate ofV tlcw of said gas. l

V,5. Calibrating apparatus comprising a container'for holding a tracer gas under pressure, a pressure chamber, afgauge for measuring the gas in` said pressure chamber,

means for supplying gas from said container to .said pressure chamber and for adjusting ,the gas pressure insaid` pressure chamber, a mixing chamber, a capillary tube connecting-said pressure chamberwith said mixing chamber, `a ltervfor removingsaid tracer gas from thesurrounding air, and means `*for supplying the surrounding. air at a ydesired rate through said filter and said mixing chamber to a receptacle-for vthe suction nozzle of=a test instrument, said gauge indicating the rate of ilow of said gasY through said capillary. c .l

Calibrating apparatus ycomprising a containerfor hQlling a tracer gas-under pressure,VA a pressure chamben a`ballas't tank connected with said pressure chamber, av

gauge for measuring the gas pressure in said pressure chamber, means for supplying gas from said container to said pressure chamber and for adjusting the gas pressure in said pressure chamber, a mixing chamber, a capillary tube connecting said pressurechamber with said mixing chamber, a filter for removing said tracer gas from the surrounding air, and means for supplying the surrounding air at a desired rate through said filter and said mixing chamber to a receptacle for the suction nozzle of a test instrument, said mixing chamber having a vent for exhausting filtered air in excess of that drawn from said receptacle by the nozzle of said test instrument..

7. Calibrating apparatus comprising a container for holding a tracer gas under pressure, a pressureY chamber, a ballast tank connected with said pressure chamber, a gauge for measuring the gas pressure in said pressure chambenmeans for supplying gas from said container to said pressure chamber and for adjusting the gas pressure in said pressure chamber, a mixing chamber, a capillary tube connecting said pressure chamber with said mixing chamber, a lter for removing said tracer gas from the surrounding air, means for supplying the surrounding air at a desired rate through said tilter to its discharge opening, a selector valve having two input ports each of which is alternately and selectively connected to one of two output ports depending on the relative positions of the valve parts, means for connecting one output port of said valve to exhaust and the other output port thereof to a receptacle for the suction nozzle of a test instrument, and a divider assembly for connecting the discharge opening of said lilter directly to one of said input ports of said valve and through said mixing chamber to the other input port thereof.

8. `Calibrating apparatus comprising a container for holding a tracer gas under pressure, a pressure chamber,

. dimensioned and said pressure being such that said flowI a ballast tank connected with said pressure chamber, a gauge for measuring the gas presure in said pressure chamber, means for supplying gas fromrsaid container to said pressure chamber and for adjusting the gas pressure in said pressure chambera mixing chamber, a capillary tube connecting said pressure chamber with said mixing chamber, a filter for removing said tracer gas from the surrounding air, means vfor supplying the surrounding air at a desired rate through said filter to its t discharge opening, a selector valve having two input ports each of which is alternately and selectively connected to one of two output ports depending on the relative positions of the valve parts, means for connecting one output port of said valve to exhaust and the other output port thereof to a receptacle for the suction nozzle of a test.

instrument, and a divider assembly for connecting the discharge opening of said lilter directly to one of said input ports of said valve and through said mixing chamber to the other input port thereof, said mxing chamber having a vent for exhausting filtered air Yin excess of that drawnY from said receptacle by the nozzle ofY said test instrument. i

9. A leak standard for providing an adjustable mass rate of owrof gas through a capillary tube to calibrate a leak detector comprising: means to'supply under pressure a tracer gas to which the leak detector is responsive,v

means to selectively adjust said pressure, means to maintain the selected pressure substantially constant includmensions to connect said ballast tank to the leak detector being'calibrated, and a gauge responsive to the said constant pressure and calibrated to indicate l,the mass'rate of Hou/,delivered to said tube, said capillary tube being is substantially according to Poiseuilles law, whereby the desired mass rate'of ow of tracer g'asmay b'e accuratelyl varied byYV adjustingthe .magnitude of said pressure.` l l 10. A leak standard for providing an adjustable lmass rate of flow of gas'through a capillary tube tocalibratc a leak detector comprising: means toA supply under pressure a tracer gas to which the leak detector is responsive, means to selectively adjust said pressure, means to maintain the selected pressure substantially constant including a ballast tank, a capillary tube of xed small internal dimensions to connect said ballast tank to the leak detector being calibrated, and a gauge responsive to the said constant pressure and calibrated to indicate the mass rate of ow delivered to said tube, said means to selectively adjust said pressure including a controlled vent from said ballast tank to bypass the gas from said tube 10 desired mass rate of ow of tracer gas may be accurately 15 varied by adjusting the magnitude of said pressure.

References Cited in the le of this patent UNITED STATES PATENTS 1,490,510 Gooley Apr. 15, 1924 2,755,663 Smith et al. July 24, 1956 2,808,294 Tamminga Oct. 1, 1957 OTHER REN-312iNCESV Article: I. New Developments in Vacuum Engineering by Jacobs et al. in Journal of Applied Physics, vol. 18, January 1947, pp. 40, 41. II. Analyzing Hydrocarbon Mixtures by Podbielniak et al. in Oil and Gas Journal, April 16, 1956, pp. 216, 217.

Publication: Bulletin of Vacuum Electronic Engineering Co., New Hyde Park, Ll., New York, on Veeco Mass Spectro-meter Leak Detector Model MS-SA, July 1953. 

